In surface-enhanced spectroscopy (SES), such as surface-enhanced Raman spectroscopy (SERS), vibrationally excitable levels of an analyte are probed. The energy of a photon can shift by an amount equal to that of the vibrational level excited by the photon (Raman scattering). A Raman spectrum, which consists of a wavelength distribution of bands corresponding to molecular vibrations specific to the analyte being probed, may be detected to identify the analyte. In SERS, the analyte molecules are in contact or close proximity, for instance, less than ten nanometers, to metal nano-particles that may be or may not be coated with a dielectric, such as silicon dioxide, silicon nitride, and a polymer, that, once excited by light, support plasmon modes (collective oscillations of free electron density), which create strong near fields around the metal nano-particles. These fields can couple to analyte molecules in the near field regions, enhancing the Raman scattering from the analyte molecules.
SERS has recently been performed to probe fluids in a specimen in vivo through implantation of the metal nano-particles subcutaneously. However, conventional devices on which SERS is performed typically include an asymmetric arrangement of the metal nano-particles in the active detecting region and thus, problems with orientation often arise with their use due to the likelihood of them being misoriented.